Class AB output stages, such as unity gain buffers, are used in various different circuits, e.g., to provide output buffers for an operational amplifier. Preferably, such unity gain buffers have low distortion, so that a low distortion operational amplifier can be achieved. In some unity gain buffer designs, where both NPN and PNP bipolar junction transistors have been available, unity gain buffers have been successfully implemented as a cascaded complementary bipolar emitter follower—often known as the ‘0002’ follower or ‘diamond’ follower.
Presently, the highest performance complementary bipolar processes, such as the Silicon Germanium BiCMOS process, are not readily available for producing complementary process bipolar junction transistors (i.e., both NPN and PNP transistors) in open market foundry bipolar processes. In any case, the NPN transistors available in open market foundry bipolar processes out-perform the complementary process transistors.